1. Field of the Invention
The present invention mainly relates to a sheet finishing apparatus for finishing (such as stapling, punching holes, or applying stamps) sheets discharged from an image forming apparatus such as a printer, a printing press, or a copier, and more particularly to a structure for a smaller and more compact finishing mechanism.
2. Description of the Prior Art
Generally, that kind of finishing apparatus is mounted to a printing device such as a printer or a copier, and is widely used for finishing sheets formed with images. A variety of methods for finishing a series of documents after being formed with images are well known in the art. Available are function units that staple documents, punch a hole therein, or even apply a stamp thereupon. These function units are arranged at a sheet discharge outlet. There is an apparatus that temporarily discharges sheets sequentially conveyed to a tray (an interim tray) for processing. After finishing a stack of sheets on the tray, the apparatus moves the stack of sheets or documents to a different tray for stacking. Another variety of such an apparatus finishes sheets in a path leading from a sheet discharge outlet to a stacking tray. The former type of apparatus is applied as a large, high-function apparatus. The latter type is used as a compact and low-cost apparatus. The present invention relates to the latter type, namely a compact and low-cost apparatus. The invention can easily be built into devices such as printers and copiers. The finishing apparatus is also configured to be smaller and more compact to be equipped at a discharge outlet of such printing or copying devices.
Japanese patents Tokkai 2003-20156 (U.S. publication US 2003/0016401 A1) and Tokkai 2002-60123 (U.S. Pat. No. 6,685,180 B1) disclose arranging a finishing unit, such as a stapler, between the discharge outlet of a device, such as a printer, and a stacking tray. Japanese patent Tokkai 2003-20156 discloses disposing a step-shaped corner support unit in a mid-position of a sheet discharged from a discharge outlet to a stacking tray. There, a series of documents (or a sheet bundle) is stapled using a stapling unit arranged at this corner support unit. Disclosed in this publication is a configuration wherein individual sheet conveyed from a discharge outlet is stacked overlapping the corner support unit and the stacking tray. The series of documents are thus stapled in that stacked state. Then, the document bundle is pushed to the top of the stacking tray where each sheet bundle is finally accumulated.
The structure arranges a member for supporting sheets on the corner over a stacking tray, and a stapling unit, and then pushes stapled sheets into a stacking tray. However, in the operation, either sheets are sequentially conveyed out from the corner support portion into a discharge tray when not finishing sheets such as by stapling them, or switching the operations for finishing by discharging offsetting sheets in the discharge outlets in a direction traversing the direction of sheet conveyance in the transport vans path and discharging them to the corner support portion and an operation for discharging sheets to a tray away from the corner support portion is necessary. Therefore, such an apparatus requires a larger stacking tray for sheets in a width direction to accommodate sheet bundle offset amounts and a mechanism for offsetting sheets.
Japanese laid-open patent 2002-60123 discloses a system for supporting the trailing edge of sheets discharged from a discharge outlet with a leading edge of a sheet stacked in a stacking tray. Disclosed are a sheet edge support member and a stapling unit for binding side edges of a sheet bundle, the trailing edge thereof supported by that support member. In this publication, after finishing a sheet bundle, such as by stapling, the sheet bundle is pushed into a stacking tray. Simultaneously, the sheet support portion rotates in a sheet accumulation direction to stack the sheet bundle in the stacking tray.
The sheet bundle is held for finishing while sheets discharged from the discharge outlet bridge between the stacking tray and the support member. After finishing is completed, the sheet bundle is stacked in the stacking tray. This enables a comparatively smaller and more compact apparatus structure. However, as an image forming apparatus, such as printer, is recently becoming smaller, there is also a demand for automated finishing for binding that is performed simultaneously to image forming. There is also a demand for wider discharge stackers than is necessary. Such a wide stacker, including the outer casing, is actually a demerit for a compact apparatus. The conventional apparatus described above has a more complex structure for offset movements of sheets discharged by discharge rollers in a direction traversing the sheet conveyance direction. There is also the problem of an inability to offset sheets with good aligning, so there is a problem of sheets being disorganized at the finishing process. After finishing a sheet bundle stacked in a stacking tray, the sheet bundle is moved in a horizontal direction over a sheet bundle already stacked. This causes the stack to collapse.